Liquid crystal materials primarily are categorized as three types. These include smectic, nematic and cholesteric liquid crystal materials. Such materials have respective characteristic structural and operational properties. For example, some types of nematic liquid crystal material are anisotropic and birefringent. Moreover, some liquid crystal materials may have characteristics of one phase, say a smectic phase, at one temperature and a different phase, say a nematic phase, at a different temperature.
One exemplary use of the birefringent characteristics of nematic liquid crystal material in a containment medium in the past has been to effect controlled scattering of incident light. For instance, if the ordinary index of refraction and the extraordinary index of refraction of the liquid crystal are, respectively, the same as and different from the index of refraction of the medium, when the extraordinary index is encountered light will refract at the interface of the liquid crystal and medium and will scatter and when the ordinary index is encountered light will be transmitted without substantial refraction or scattering. Moreover, pleochroic dye has been used together with nematic liquid crystal material that is responsive to a prescribed input to dye, to filter or to absorb light as a function, for example, of structural characteristics of the liquid crystal material and dye.
Smectic liquid crystals are characterized by a structure which is generally laminar. Smectic liquid crystal materials have not been used until recently, and then in the limited construction of display devices and some memory devices. Smectic phase generally occurs at a temperature which is lower than the corresponding nematic or cholesteric phases that often are associated with optical applications. Earlier smectic liquid crystal materials were not used because the nature of the smectic phase makes it more difficult to align or to arrange the liquid crystal structure than the higher temperature phases.
The Kerr effect, more precisely the electrooptical Kerr effect, is a birefringence that is induced electrically. The basis of the Kerr effect theory is documented in various texts. Examples are Light by R. W. Ditchburn, Academic Press (London, 1976) and Optics & Lasers by Matt Young, Springer-Verlag (New York, 1984). The entire disclosures of such books are hereby incorporated by reference.
Light is a term by which reference is made to a form of electromagnetic radiation generally in a particular wavelength band or frequency range. In the context of the present invention light is used to refer to such electromagnetic radiation in the visible, ultra-violet and infrared ranges. Generally, the reference to light and to electromagnetic radiation herein means that electromagnetic radiation that will operate in accordance with the principles of the present invention.